P.K. Is what I would call on of the best one-on-one defenseman in the league. As a coach, when you want to shutdown ONE player, you want a player like Subban. I don't think Maclean's think like this with Karlsson. As a coach you need a goal, you want Karlsson on the ice. Yet, P.K. is also this kind of player. As a coach if thing's get rough and chippy, you expect Subban to be in his game, Karlsson not much.
Karlsson benefit's from the player's he play's with (I.E. Big phisical player) Subban's benefit's from himself.

Is Karlsson the best Offensive dman in the league ? Debatable...
Is P.K. the best offensive Dman in the league? Not at all.

I think it's dumb to compare Subban to Karlsson has their purpose are not the same. One is expected to be the one who drive's your offense. The other one is expected to drive the team.